Glacial System of Himalaya and PDGL impacts, cause and mitigation measures

1. Glacial System & Environmental
Change
Fluvioglacial Sedimentation
Glacier Outburst Flood (GLOF),
Slope Movements,
Impact on upland sediment systems
Management and Remediation
Presenter
Sujan Raj Pandey
Roll No. 05
M.Sc. 2nd Semester

2. Talk Outline
• Glacial System
• Glacial System and Environmental change
• Changes in Sedimentation
• Supraglacial and Subglacial drainage
• Fluvioglacial sedimentation
• A subglacial outburst flood: Jökulhlaup
• Types of Glacial Lake
• Glacial lake in Nepal Himalaya
• Glacier Lake Outburst Flood
• Potentially Dangerous Glacial Lake (PDGL)
• Case Studies of Imja Lake, Tsho Rolpa, Thulagi and Lower Barun Lake
• Slope movements
• Cause of slope instability in the Himalaya.
• Increase in landslide after the Gorkha earthquake.
• Seti River Rock avalanche in Nepal.
• Anthropogenic Impact on upland sediments systems
• Management and Remediations.
• Hazard assessment and Mapping techniques
• Mitigation Measures

3. Glacial System
• A characteristic feature of many mountainous environments is the presence of
glacier ice.
• A glacier is a large body of ice that is moving from a higher to a lower elevation.
• Glaciers can be viewed as a system with its balance between inputs, storages,
transfer and output of mass.
Figure 1: A model of Glacial System

4. • The main storage is ice
but also debris that are
distributed at top, within
and at base of the glacier
and are transported
as moraine.
• The output is mainly
meltwater and calving
sections of ice. This
meltwater transports
debris from within the
glacier.
Figure 2: Glacier as a system.

5. • Accumulation exceeds
ablation then the glacier
will advance.
• If the ablation exceeds
accumulation then the
glacier will retreat.
• Lost ice is replaced by ice
from the accumulation zone
through transport of ice
from the upper part to the
lower part with the help of
gravity.
Figure 3: A conceptual model of mass balance in glacial system

6. Glacial System and Environmental change
a) Changes in the amount or timing
of precipitation
b) The amount of melting due to
warming and layer of debris
present.
c) Recent warming of global climate
has reduced accumulation and
increased ablation (output) levels.
• The glacier mass balance varies based on environmental factors:
Ice loss relative to 1970 for the glaciers based on
data from the WGMS.
• Associated Hazards:
glacier fluctuations,
glacier outburst floods and
avalanches

7. Changes in Sedimentation
• Sediment stores in mountain environments are fundamental in controlling
basin sediment yield and may be sensitive to environmental changes in climate
and/or human disturbance.
• Sediment yield rates are likely to vary
(i) within a same glacier setting during multiple glacial cycles.
(ii) between different glacier settings during the same glaciation.
(iii) Due to changes in ice thickness, velocity erosion rates, meltwater
transport capacity and sediment at the bed.

8. Figure 4: A
conceptual
model of the
variability in
sediment yield
from glaciers
over multiple
glacial cycles
(Antoniazza and
Lane, 2021)

9. Figure 5: A conceptual model of change in sediment yield during phases of glacier advance, stagnation, retreat
and re-advance

10. Supraglacial and Subglacial drainage
Supraglacial Subglacial
Similar to stream flow in all surface environment. Stream flow or lake below the glacier.
Stream are enriched with meltwater resulted from
ablation of firn or rain water (sometimes) and
flows from higher areas to lower areas under
gravity.
Stream are enriched with meltwater generated by
basal sliding, geothermal heat flux of earth,
pressure from weight of ice mass above,
supraglacial meltwater drawn by gravity through
crevasse or moulins.
Supraglacial meltwater are enriched in summer
which provide input for subglacial drainage.
Subglacial meltwater dominates the winter with
supraglacial inputs isolated.
Forms glacial ice lake, moraine dammed lake at
the surface of the glacier, large supraglacial lakes
results during the summer which when breached
causes GLOF hazards.
Meltwater ponds in depression underneath
glacier ice forming subglacial lakes which
influence ice flow, basal sliding and when
breached causes catastrophic Jökulhlaup and
glacial surge.

11. Figure 6 : A schematic illustration for different glacial drainage system.

12. Fluvioglacial sedimentation
• In fluvioglacial environment
the discharge fluctuates and,
consequently, the transport
capacity varies.
• Result in sudden changes in
the particle sizes and rapid
variations of sedimentary
structures, both laterally and
vertically
• This is emphasized by the
continuous erosion that
affects sedimentation in
areas of retreating and
advancing glaciers.

13. • Decrease in the transport
capacity of the ice melt
water as it discharge
through glacier snout
resulting an outwash
plain deposits or sandur.
• During the stages of
glacial retreat, the
proximal areas of the
sandur are eroded and
new sandur develop from
the previous ones.

14. • Glacial (Gl) and glacio-fluvial (Gf)
features have been identified as
the marker morphological zones
which provides information about
pattern of retreat and ELA.
• The glacial zone contains the
primary sediments and provides
information about the pattern of
retreat and ELA.
• The glacio-fluvial outwash plain
exhibits modification of glacial
signatures and often contains
secondary sediments.

15. A subglacial outburst flood: Jökulhlaup
• An Icelandic term that
describe catastrophic
flood caused by the
sudden drainage of a
subglacial or ice-
dammed lakes.
• One of the key triggers
for Jökulhlaup is the
eruption of a volcanic
beneath an icecap.
Figure: Subglacial conceptualization of jökulhlaup thermodynamics, Spring
and Hutter [1981]. (Q and Pw signify discharge and hydrostatic pressure,
respectively.

16. Video of a jokulhlaup cascading off the margins of the Eyjafjallajokull volcano
on 14th April 2010, Iceland.
• As a consequence of the
water release river levels
may rise by up to 10 m
and millions of cubic
metres of sediment are
deposited, often raising
sandur.
• Björnsson (2003)
estimates the sediment
load of a large
jökulhlaup may be as
great at 10 × 106
ton per
event.

17. Types of Glacial Lake
Glacial Lake type Definition
A. Moraine- dammed
lake (M), M(e), M(I),
M(Ig)
Lake dammed by moraine
following glacial retreat
B. Ice- dammed lake (I)
a) Supra-glacial lake
(Is)
b) Glacier ice-dammed
lake (Id)
-Lakes dammed by glacier ice
-Pond or lake on the surface of
glacier
- Lake dammed by glacier ice with
no moraines
C. Glacier erosion
lake(E)
a) Cirque lake (Ec)
b) Glacier trough
valley (Ev)
Bodies of water that form as a
result of glacial erosion process
which accumulated after glacier
has retreated or meltaway
D. Others glacial
lake(O)
O(I)
Lakes formed in a glaciated valley,
and fed by glacial melt.
-Debris-dammed lake

18. Glacial lake in Nepal Himalaya
• Supra-glacial lakes generally form on the
surface of glaciers that are almost
entirely covered by a thick mantle of
debris and have low gradients or
stagnant.
• As lake expansion and glacial retreat
continue, these supra-glacial lakes may
merge with end-moraine dammed lakes.
• Moraine-dammed lake forms as a glacier
retreats, and meltwater fills the space
between the proglacial moraine and the
retreating glacier.

19. Imja Lake is a typical example of a moraine-dammed
lake that has developed from a supraglacial lake
• As these lakes increase in size and deepen,
the presence of open water in contact with
the glacier terminus further accelerates
glacial retreat and thinning and may give
rise to increasing instability.
• The largest of the existing glacial lakes in
Nepal are those that began as a series of
supra-glacial meltwater ponds. They
include;
i. Tsho Rolpa,
ii. Imja Tsho, and
iii. Thulagi Lake.
• All of which began to form some 50 to 60
years ago.

21. Figure: 5 Decadal expansion km2/decade of
glacial lake from 1987 to 2017 from different sub-
basins of the major river basins in Nepal.
Source: Glacial Lakes in the Nepal Himalaya: Inventory and
Decadal Dynamics (1977–2017) Nitesh Khadka et al., 2018

22. Glacier Lake Outburst Flood
• Meltwater lakes are potentially unstable; the
sudden catastrophic release of water from
such a lake is known as a glacial lake
outburst flood (GLOF).
• There are two distinctly different forms of
glacial lake outbursts:
a) those that result from the collapse or
overtopping of ice dams formed by the
glacier itself and
b) those that occur when water drains
rapidly from lakes formed either on the
lower surface of glaciers (supra-glacial)
or between the end moraine and the
terminus of a retreating glacier
(moraine-dammed).
Animated video of GLOF by ICIMOD.

25. Potentially Dangerous Glacial Lake (PDGL)
• Out of 3624 glacial
lake mapped, 1410
lakes are considered
large enough to
cause serious
damage. 47 lakes
were considered
PDGL.
• The PDGLs were
ranked to determine
the priority for
potential GLOF risk
reduction.
Based on recent study of ICIMOD 2020

26. Potentially Dangerous Glacial Lake (PDGL)
• Since 1977, Nepal has experienced 26 GLOF events of which 14 originated in the
country. And, with the changing climate resulting in increasing rate of glacial melt,
GLOF remains an ever-present threat for Nepal.
• The identification of PDGL,
and the ranking of the PDGLs
will be useful in designing
GLOF risk management and
reduction strategies in
Nepal.
• Water levels had earlier been
lowered in four lakes to
reduce the risk of GLOFs ―
Tsho Rolpa and Imja Tsho in
Nepal, and 2 in the TAR,
China

27. • The area of the lake was 1.055𝑘𝑚2
as of 2009
while the lake area has been increased to
1.5𝑘𝑚2
as of present.
• Low possibility of a rock-fall or rock-slope
failure
• The end moraine damming the lake is 536 m
wide and 567 m long; any overtopping waves
would have to overcome this wide barrier.
• The construction of sluice gate by UNDP, lower
the water level by 3.4m
Case Study of Imja Tsho Glacier and associated
GLOF
Lhotse Nup
Glacier Lhotse
Glacier
Imja
Glacier
Imja Lake
The inauguration of the Imja Lake channel and sluice gate
in 2016. Photo: UNDP

28. Case Study of Tsho Rolpa Glacier and associated GLOF
• In 1950, Tsho Rolpa were group of six small
supraglacial ponds with area of 0.23𝑘𝑚2
while the lake
grew from 1960s to 1990s to such extent that could
breach its end moraine.
• At present, Tsho Rolpa Glacial Lake covers about of
1.85𝑘𝑚2
area.
Growth of Tsho Rolpa Glacier Lake

29. Possible Triggers for Tsho Rolpa GLOF events
• Tsho Rolpa has narrow end moraine where new
channels are being developed inside the moraine due
to seepage and leading to instability.
• Seismic events and mass movements.
• Hanging glacier and its movement.
Mitigations for Tsho Rolpa
GLOF events
• Regular monitoring
• Sluice Gate that reduces level of
water by 3m.
• Safety Measures and Awareness to
villages below.

30. Case Study of Thulagi Glacial Lake and associated GLOF
Figure: Overview of Thulagi Glacier and glacial lake in 1992
photo (left) and 2009 December Quick Bird image (right); the
red line shows the expanded area
• Thulagi Lake began to form about 50 years ago
when small supra-glacial lakes began to enlarge
and coalesce. It is now more than 2 km long.
• Thulagi Glacier is a long, debris-covered glacier
with a 40 m high terminal cliff where ice calving is
a regular phenomena.
• Scientists monitoring Thulagi have found the
glacier has receded by 2km since 1984, the ice
replaced by a lake.
• In the Gandaki Basin is the particularly dangerous
Thulagi glacial lake below Himalchuli, which
would directly threaten three major hydroelectric
projects along the Marsyangdi River.

31. Figure 7.18: Comparison of lake development from images,
topographical maps, and field investigation data for the Imja Tsho,
Tsho Rolpa, and Thulagi Lakes. Imja lake grew at a slower rate up to
2000 when the rate increased; the growth rate of Tsho Rolpa
diminished substantially after mitigation in 2000
Figure 7.19: The relationship of volume and depth for
the Tsho Rolpa, Thulagi, and Imja lakes.

32. Case Study of Lower Barun Glacial Lake and associated GLOF
• The Lower Barun lake was formed by the
gradual recession of the Barun Glacier and
by meltwater pooling in front of the
moraine complex.
• The lake has shown substantial area growth
from 0.04𝑘𝑚2 𝑖𝑛 1975 𝑡𝑜 2.09𝑘𝑚2at present.
• With gradual erosion of the lake’s lateral
moraine, the Barun Khola riverbed is
almost the same height as the moraine.
• Regular Monitoring of Lower Barun Lake is
recommended.
An evolution of increasing Lower Barun Lake.
(Source: ICIMOD, 2021)
Altitude: 4550m
Length: 2.7km long and
Width: 600m wide
Moraine Dammed -Proglacial Lake.

33. Source: Journal of Hydrogeology. 598(6):126208
Overview of the study area showing Lower Barun Glacier and
Lower Barun Lake located in the Barun Khola basin, Nepal.
Cross-sectional profile of Lower Barun glacier and lake structure;
Flow depth (m), and (b) Flow velocity (m s 1 ) of the two modeled potential avalanches; (c)
modeled impulse waves and overtopping (Evers et al., 2019); (d) photograph showing the
steep slope (avalanche source zone) located at the right surrounding slope, the modeled
avalanche trajectory, and the impact site on the lake

34. Slope movements
• Mass wasting of slopes in mountain environments proceeds by a combination of small-
scale processes and infrequent large-scale events.
• Some mass movements led to landslide dam outburst flood (LDOF) E.g.: Larcha, upper
Bhotekoshi Valley
Avalanche along Kapuchhe Glacier

35. Cause of slope instability in the Himalaya.
• Primary cause of failure is force of gravity along
with rock and soil type and strength, rock structure,
soil depth, change in slope gradient due to tectonic
uplift, porosity and permeability.
• Secondary cause of failure are seismicity,
intensity of precipitation, landuse, natural slope
condition, weathering condition, gullies, rivers,
ground surface temperature and groundwater
conditions.
• Anthropogenic cause of failure during road and
construction activities, improper landuse,
agricultural practices, overgrazing and
deforestation.

36. Increase in landslide after the Gorkha earthquake
• The Gorkha earthquake (M w 7.8) of
April 25, 2015, triggered many
catastrophic landslides and avalanches.
• The largest and most destructive
landslide triggered by the Gorkha
earthquake occurred in the Langtang
valley , where the shaking triggered a
debris avalanche composed of ice, snow
and soil, burying several villages, and
killing at least 350 people.
Figure: Changes in mapped landslide numbers and total landslide area between
2014, the Gorkha earthquake in 2015, and post-monsoon 2019, from Rosser et
al. (2021).
Vertical blue bars show the timing of the monsoon; solid black line is landslide
number; dashed black line is landslide area; and, the time of the earthquake
(orange line) and the first local elections (green lines).

37. Seti River Rock avalanche in Nepal.
• In early May 2012 an enormous rockfall
occurred on the flanks of Annapurna IV in
Nepal, triggering a debris flow that traveled
rapidly down the Seti River towards the town
of Pokhara.
• The small rockslide downstream played a key
role in damming of lake and cause LDOF.

38. GLOF caused by Earthquake.
• The Gorkha Earthquake imposed an
avalanche of ice and rock froms Tengi
Ragi Tau Mountain and cascaded into
Dig Tsho.
• This created 4.2-8.2m high surge wave
across the lake.
• Fresh mud and sand deposits on
vegetation.
• The flood destroyed two small bridges
downstream and damaged a third,
larger bridge at Thametang, where the
flood height peaked at about 1.5 m.
Figure 4. (a) Ice avalanche source areas above Dig Tsho, (b) lake outlet showing approximate path
of the surge wave, and (c) measured heights of surge wave along shores of Dig Tsho. There was no
significant lowering of the outlet and no subsequent change to future flood hazard.

39. Anthropogenic Impact on upland sediments systems
Himalayan environmental degradation theory (HEDT): Ives and Messerli (1989)
illustrated how changes in population structure and pressure (human impacts) on a
mountain environment can lead to a change in the natural sedimentary system.
The qualitative model is deceptively simple and can be summarized as :
• Population growth (Macro level)
• Population expansion results in massive deforestation. (Meso-scale)
• Soil erosion and landslides. (Micro to Meso Scale)
• Increased runoff and flooding. (Macrolevel)
• Positive feedback – accelerated deforestation and greater soil loss
• Degraded soil structure. (Microscale)

40. Figure: General summary of the key elements of the Himalayan
environmental degradation theory as proposed by Ives & Messerli
(1989). Schematic diagram showing the relationship between human-
induced and natural processes at the micro-, meso- and macro-levels.
• Landslides are very common
along the over 44,000 km long
road network of the Himalayan
region.
• The increasing population
pressure has forced people to
drastically change land use.
• Forest, grasslands and pastures
are being converted into
agricultural land.

41. • Laban (1978, 1979) has
shown that very high soil
erosion rates in Nepal
can be tolerated within
the landscape and half
the landslides are from
natural causes.
• Accelerated erosion due
to agriculture and
deforestation have
increased erosion rates
by a factor of five to ten
(Rawat & Rawat 1994).

42. • Under the prediction of a warming scenario for the Alps the following are all
likely consequences (Zimmermann & Haeberli 1992; Haeberli 1995):
1) greater frequency of outburst floods and glacier hazards;
2) permafrost degradation and slope instability increased debris flow activity;
3) decline in material strength of foundations of high mountain buildings;
4) damage to reservoir systems (damage to infrastructure)and increased
sedimentation rates (reduced storage capacity).

43. Management and Remediations.
• Environmental sedimentology is an essential element in the management and
remediation of sediment related hazards in mountain region which implies through;
a) Hazard assessment & Mapping techniques
b) Monitoring and
c) Mitigation Measures
• Disaster risks are a function of interplay among three key elements: hazards,
exposure, and vulnerability.

44. Hazard assessment and Mapping techniques
• Mountain Environment posses high geomorphological processes resulting
unstable terrain. Any move to develop such areas results in a potential hazard.
• Mountain hazards are on the increase due to increasing development pressures
and recent environmental change.
• Slope instability in mountainous terrain is a natural occurrence. In many
regions, however, this represents an important hazard that needs to be carefully
assessed.
• Detailed GLOF hazard and risk assessment is undertaken by simulating GLOF
scenarios.

45. Hazard
Identification
Hazard
Assessment
Mapping
Hazards
Monitoring &
Risk
management
Landuse
planning or
Mitigation
Classification of
landslides, GLOF
mapping of landslide
phenomena and a
register of slope
instability events.
Determination of the
magnitude or
intensity of an event
over time and pre
modelling scenarios
of GLOF
Provides degree of
danger and alert for
preparedness with
color code.
involves direct
measurements of the
of a river, slope or
glacier
-activate a warning
and evacuation
system.
-utilizes the hazard
map, which is the
basic document for
land-use planning,
-feeds directly into
the local authority
planning process

46. Mitigation Measures
• The prone hazard of Himalaya are landslide, floods and GLOF such that an
integrated approach is needed to mitigate these problems.
• Foremost a regional level hazard and susceptibility map are to be prepared.
• Landslide and GLOF inventories along with future predicted modelling provides idea
for potential hazards.
• Landslide can be mitigate by retaining walls, bioengineering, rock bolts while
gradual monitoring and draining of glacial lake can reduce risk of GLOF.
• Flood control measures downstream to mitigate the effects of the flood.
• Awareness and preparedness of hazard are most.

47. Periglacial Environment and Permafrost Regions.
• The periglacial environment is a cold climate, frequently marginal to the glacial
environment, and is characteristically subject to intense cycles of freezing and thawing
of superficial sediments.
• Permafrost is any ground that
remains completely frozen—32°F
(0°C) or colder—for at least two
years straight.
• However, processes that involve
the freezing, unfreezing, and
movement of water are considered
to be periglacial; processes
associated with the presence of
perennially frozen ground are
permafrost.

48. • A periglacial landform is a feature resulting from the action of intense frost, often
combined with the presence of permafrost.
Processes in Periglacial environment.
a) freeze-thaw weathering results in
frost-shattered boulders, snow
hollows, blockfields sorted stone
polygons and stripes, and surface
cracks.
b) Slope processes resulting solifluction
lobes
c) Thermokarst landscape.

49. Pingo Hummocky due to ice in ground
A talus or scree slope
Permaforst Polygons
Block fields Solifluction

50. Permafrost Distribution in Hindu Kush Himalaya
Permafrost distribution in HKH: Spatial
patterns of agreement between mapped
rock glaciers and PZI (Schmid et al., 2015)

51. Periglacial Hazards in Permafrost Area
• When permafrost thaws, slopes become more vulnerable
to erosion.
• Debris and sediment may deposit slowly in nearby rivers
or slide downhill catastrophically, destroying homes,
bridges and roads.
• Loss of permafrost can increase the likelihood of GLOF or
rockfalls.
• Ground ice degrades and the soil surface collapses.
• Landslides and floods.
Massive ice wedge exposed in
research tunnel into permafrost
near Fairbanks, Alaska

52. Periglacial Hazards in Permafrost area
Usteq—a catastrophic form of permafrost thaw collapse—
claimed this cabin at Elson Lagoon, Alaska. Photo credit: U.S.
Geological Survey.
• Ground subsidence.
• Lake dissapperances or new lake
developments.
• Encroachment into aquifers and surface
waters.
• Releases greenhouse gases like carbon
dioxide and methane to the atmosphere

53. Climatic and Anthropogenic impacts on periglacial regions
• Increases in air temperature,
modification in the ground
thermal regime and surface
energy balance
=
ground warming, changing
runoff and alterations in the
freeze-thaw cycles.
• Under anthropogenic
warming, infrastructure
damage is projected to
continue.

54. Conceptual diagram showing
links between hydroclimate
effects of global warming and
sedimentary and geomorphic
response

55. Mitigation of Hazards in Periglacial Regions
• Early identification of the susceptibility of a site to periglacial geohazards.
• Permafrost carbon monitoring and modeling.
• Implementation of open cuts and artificial dams.
• Convection embankments, thermosyphons and piling foundations, have been proven
success at preserving and cooling permafrost and stabilizing infrastructure.
• More research on periglacial region under risk.
• Awareness and Preparedness

56. Thank You ☺